https://gcc.gnu.org/g:ed6d11c16d69b1cf388bfa6dbc00fa3b34ade969
commit ed6d11c16d69b1cf388bfa6dbc00fa3b34ade969
Author: Jeff Law <j...@ventanamicro.com>
Date: Fri Jul 26 17:30:08 2024 -0600
[RISC-V][target/116085] Fix rv64 minmax extension avoidance splitter
A patch introduced a pattern to avoid unnecessary extensions when doing a
min/max operation where one of the values is a 32 bit positive constant.
> (define_insn_and_split "*minmax"
> [(set (match_operand:DI 0 "register_operand" "=r")
> (sign_extend:DI
> (subreg:SI
> (bitmanip_minmax:DI (zero_extend:DI (match_operand:SI 1
"register_operand" "r"))
> (match_operand:DI 2
"immediate_operand" "i"))
> 0)))
> (clobber (match_scratch:DI 3 "=&r"))
> (clobber (match_scratch:DI 4 "=&r"))]
> "TARGET_64BIT && TARGET_ZBB && sext_hwi (INTVAL (operands[2]), 32) >= 0"
> "#"
> "&& reload_completed"
> [(set (match_dup 3) (sign_extend:DI (match_dup 1)))
> (set (match_dup 4) (match_dup 2))
> (set (match_dup 0) (<minmax_optab>:DI (match_dup 3) (match_dup 4)))]
Lots going on in here. The key is the nonconstant value is zero extended
from
SI to DI in the original RTL and we know the constant value is unchanged if
we
were to sign extend it from 32 to 64 bits.
We change the extension of the nonconstant operand from zero to sign
extension.
I'm pretty confident the goal there is take advantage of the fact that SI
values are kept sign extended and will often be optimized away.
The problem occurs when the nonconstant operand has the SI sign bit set.
As an
example:
smax (0x8000000, 0x7) resulting in 0x80000000
The split RTL will generate
smax (sign_extend (0x80000000), 0x7))
smax (0xffffffff80000000, 0x7) resulting in 0x7
Opps.
We really needed to change the opcode to umax for this transformation to
work.
That's easy enough. But there's further improvements we can make.
First the pattern is a define_and_split with a post-reload split condition.
It
would be better implemented as a 4->3 define_split so that the costing model
just works. Second, if operands[1] is a suitably promoted subreg, then we
can
elide the sign extension when we generate the split code, so often it'll be
a
4->2 split, again with the cost model working with no adjustments needed.
Tested on rv32 and rv64 in my tester. I'll wait for the pre-commit tester
to
spin it as well.
PR target/116085
gcc/
* config/riscv/bitmanip.md (minmax extension avoidance splitter):
Rewrite as a simpler define_split. Adjust the opcode appropriately.
Avoid emitting sign extension if it's clearly not needed.
* config/riscv/iterators.md (minmax_optab): Rename to uminmax_optab
and map everything to unsigned variants.
gcc/testsuite/
* gcc.target/riscv/pr116085.c: New test.
(cherry picked from commit 6e5aae47e3b910f9af6983f744d7a3e2dcecba1d)
Diff:
---
gcc/config/riscv/bitmanip.md | 38 +++++++++++++++++++------------
gcc/config/riscv/iterators.md | 9 ++++----
gcc/testsuite/gcc.target/riscv/pr116085.c | 29 +++++++++++++++++++++++
3 files changed, 58 insertions(+), 18 deletions(-)
diff --git a/gcc/config/riscv/bitmanip.md b/gcc/config/riscv/bitmanip.md
index 9fc5215d6e3..b19295cd942 100644
--- a/gcc/config/riscv/bitmanip.md
+++ b/gcc/config/riscv/bitmanip.md
@@ -549,23 +549,33 @@
;; Optimize the common case of a SImode min/max against a constant
;; that is safe both for sign- and zero-extension.
-(define_insn_and_split "*minmax"
- [(set (match_operand:DI 0 "register_operand" "=r")
+(define_split
+ [(set (match_operand:DI 0 "register_operand")
(sign_extend:DI
(subreg:SI
- (bitmanip_minmax:DI (zero_extend:DI (match_operand:SI 1
"register_operand" "r"))
- (match_operand:DI 2
"immediate_operand" "i"))
- 0)))
- (clobber (match_scratch:DI 3 "=&r"))
- (clobber (match_scratch:DI 4 "=&r"))]
+ (bitmanip_minmax:DI (zero_extend:DI
+ (match_operand:SI 1 "register_operand"))
+ (match_operand:DI 2 "immediate_operand")) 0)))
+ (clobber (match_operand:DI 3 "register_operand"))
+ (clobber (match_operand:DI 4 "register_operand"))]
"TARGET_64BIT && TARGET_ZBB && sext_hwi (INTVAL (operands[2]), 32) >= 0"
- "#"
- "&& reload_completed"
- [(set (match_dup 3) (sign_extend:DI (match_dup 1)))
- (set (match_dup 4) (match_dup 2))
- (set (match_dup 0) (<minmax_optab>:DI (match_dup 3) (match_dup 4)))]
- ""
- [(set_attr "type" "bitmanip")])
+ [(set (match_dup 0) (<uminmax_optab>:DI (match_dup 4) (match_dup 3)))]
+ "
+{
+ /* Load the constant into a register. */
+ emit_move_insn (operands[3], operands[2]);
+
+ /* If operands[1] is a sign extended SUBREG, then we can use it
+ directly. Otherwise extend it into another temporary. */
+ if (SUBREG_P (operands[1])
+ && SUBREG_PROMOTED_VAR_P (operands[1])
+ && SUBREG_PROMOTED_SIGNED_P (operands[1]))
+ operands[4] = SUBREG_REG (operands[1]);
+ else
+ emit_move_insn (operands[4], gen_rtx_SIGN_EXTEND (DImode, operands[1]));
+
+ /* The minmax is actually emitted from the split pattern. */
+}")
;; ZBS extension.
diff --git a/gcc/config/riscv/iterators.md b/gcc/config/riscv/iterators.md
index 734da041f0c..0a669f560e3 100644
--- a/gcc/config/riscv/iterators.md
+++ b/gcc/config/riscv/iterators.md
@@ -327,10 +327,11 @@
[(plus "add") (ior "or") (xor "xor") (and "and")])
; bitmanip code attributes
-(define_code_attr minmax_optab [(smin "smin")
- (smax "smax")
- (umin "umin")
- (umax "umax")])
+;; Unsigned variant of a min/max optab.
+(define_code_attr uminmax_optab [(smin "umin")
+ (smax "umax")
+ (umin "umin")
+ (umax "umax")])
(define_code_attr bitmanip_optab [(smin "smin")
(smax "smax")
(umin "umin")
diff --git a/gcc/testsuite/gcc.target/riscv/pr116085.c
b/gcc/testsuite/gcc.target/riscv/pr116085.c
new file mode 100644
index 00000000000..998d82bd235
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/pr116085.c
@@ -0,0 +1,29 @@
+/* { dg-do run } */
+/* { dg-require-effective-target rv64 } */
+/* { dg-options "-march=rv64gc_zbb -mabi=lp64d -fno-ext-dce" } */
+
+extern void abort (void);
+
+int a = 2;
+unsigned b = 0x80000000;
+int arr_5[2][23];
+void test(int, unsigned, int);
+int main() {
+ test(a, b, 1);
+ if (arr_5[1][0] != -2147483648)
+ abort ();
+ return 0;
+}
+
+#define c(a, b)
\
+ ({
\
+ long d = a;
\
+ long e = b;
\
+ d > e ? d : e;
\
+ })
+__attribute__((noipa))
+void test(int f, unsigned g, int h) {
+ for (int i = 0; i < h; i = f)
+ arr_5[1][i] = h ? c(g, 7) : 0;
+}
+
